(a) Field of the Invention
The present invention relates to a communication system. More particularly, the present invention relates to a transmitting apparatus for enabling a receiving apparatus to measure a radio channel with increased accuracy in a communication system.
(b) Description of the Related Art
Generally, a communication system can operate properly when the system is designed to be suitable for a channel to be used. Therefore, it is important to understand characteristics of a channel used in the communication system in order to design the system.
The next generation wireless communication system needs a high data transmission speed because its aims include not only transmission of voice but also transmission of multimedia data. To accomplish a high speed data rate, various methods are currently being researched and developed (e.g., use of wideband frequency, multiple antennas, etc.).
A communication system using multiple antennas reacts to channel characteristics more sensitively than does a communication system using a single antenna. Accordingly, it is very important to understand the channel characteristics when designing the system using the multiple antennas.
A radio channel measuring system (radio channel sounder) measures a channel by using a pre-designated signal which is designated by a transmitting terminal and a receiving terminal. Such a channel measurement is performed by the receiving terminal. When a signal transmitted by the transmitting terminal through an antenna reaches the receiving terminal after passing through a radio channel, the receiving terminal correlates the pre-designated signal and obtains a channel measuring result. This channel measurement method has been used broadly since the 1980's.
When radio channel measurement first started, an analogue type of radio channel measurement system was primarily used. However, since the middle of the 1990's when digital technology was being developed, a digital radio channel measuring system has been dominantly used. But the digital radio channel measurement system actually uses an analogue type of signal in transmitting and receiving, so analogue elements such as an analogue filtering and amplifying unit are included in the communication system. Therefore, the communication system itself has its own impulse response, and the impulse response affects radio channel measurement values.
FIG. 1 shows a conventional communication system for radio channel measurement.
As shown in FIG. 1, the communication system for radio channel measurement includes a transmitter 10, a radio channel 20, and a receiver 30. The transmitter 10 includes a pseudo-noise (PN) code generator 12 for diffusing a transmission signal in a PN code, a binary phase shift keying (BPSK) modulator 14 for BPSK-modulating the diffused signal, a pulse shaper 16 for shaping the modulated signal, and an analogue filtering and amplifying unit 18 (high power amplifier, HPA) for filtering the pulse shaped signal and amplifying the same. The receiver 30 includes an analogue filtering and amplifying unit 32 (low noise amplifier, LNA) for filtering and amplifying the signal received through the radio channel 20, a receiving filter 34 for filtering the amplified signal, and a correlating detector 36 for correlating the filtered signal with the PN code and calculating an estimated channel value.
Here, an original characteristic of the communication system generally means some kinds of nonlinearities of filters and elements included in the transmitter 100 and receiver 300. The original characteristic of the communication system interferes with accurate channel measurement. In more detail, it causes a distortion of channel value and a reduction of system resolution. Therefore, the original characteristic of the communication system needs to be compensated or eliminated in order to increase accuracy of the radio channel measurement.
In 1991, P. C. Fannin et al. proposed a matched filter (MF) method for compensating such an original characteristic of the communication system. This method is for equalizing an original impulse response of the communication system by using the MF considering the original impulse response (refer to P. C. Fannin, A. Molina, S. S. Swords and P. J. Cullen, Digital signal processing techniques applied to mobile radio channel sounding, IEE Proceedings F, Radio and Signal Processing, vol. 138, pp. 502-508, October 1991).
In 1997, T. Korhonen et al. proposed a method in which a matched filter deconvolution (MFD) method having better performance is used with a polynomial compensation method. The MFD method can increase resolution by sacrificing signal-to-noise ratio (SNR), and the polynomial compensation method prevents a loss of SNR by decreasing deconvolution noise occurring in a MFD process. This method cannot compensate the original characteristic of the communication system, but compensates a channel measurement error caused by a characteristic of PN code (refer to T. Korhonen and S-G. Haggman, Deconvolution Noise in DS-Radio Channel Sounding and a Polynomial Compensation Method, IEEE PIMRC '97, vol. 3, pp. 806-810, September 1997).
The prior arts mentioned above have drawbacks in that they cannot provided accurate measurement of a channel because they reduce system performance by amplifying noise, and they cannot compensate the original characteristic of the communication system. In addition, an operation burden is increased because compensation of the receiver 300 needs to be performed on the received signal.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.